The field of this invention relates to thermoplastic polymers, especially PET, which are modified to improve their heat-up characteristics while maintaining viable color and low haze.
Heretofore, various compositions have been prepared to reduce the heat-up time in preforms before they are blown into containers for food or beverages. This reduction can be affected by adding components to a thermoplastic polymer, like PET, to increase its ability and efficiency to absorb electromagnetic radiation (EMR) during heat-up. These additives, however, cannot have a substantial negative impact on color or haze properties of the resultant PET bottle or container.
One attempt to reduce heat-up time in PET was taught in Pengilly U.S. Pat. No. 4,408,004 by providing a high clarity, low haze polyester containing carbon black. More recently, use of graphite has been found to be a more effective additive than carbon black in this regard.
Certain iron oxides may also accomplish this function. For instance, U.S. Pat. No. 4,420,581 discloses the use of Fe2O3 (red iron) for this purpose. In International Publication No. WO 99/37708, a disclosure is made that Fe3O4 may be even more effective than Fe2O3. Finally, U.S. Pat. Nos. 4,408,004 and 5,419,936 incorporate elemental antimony, produced by the action of a reducing agent on the antimony polymerization catalyst, to reduce heat-up times.
None of these disclosures incorporate a compound, especially an iron alloy, where the iron in the iron compound is inert or chemically unreactive with the polymer or with any other additive to the polymer. Thus, the need continues to exist for such a composition of matter.
The discovery of this invention comprises a thermoplastic polymer, exemplified by poly(ethylene terephthalate) (PET), having its heat-up rates drastically improved while not substantially adversely affecting its color properties or haze content. By the term xe2x80x9csubstantially adversely affectingxe2x80x9d, it is meant that these properties are maintained at or below the desired levels for useful compositions. Generally, this means that, on a preform, L*, a* and B* values should be maintained in a tolerable range wherein preform L* is less than 60, and the a* (red/green value) and b* (blue/yellow value) should be close to neutral (0) or minus values, and not greater than plus 3.0 or plus 7.0, respectively. For production of acceptable preforms and bottles, preform haze values should be kept below 60%, and bottle haze values should be kept below 6%.
Thus, the invention is specifically directed toward PET with an inert iron compound selected from iron phosphide, iron silicide, or combination thereof, in a quantity effective to reduce heat-up time, but not large enough to negatively impact qualities of L*, b*, and a* color properties or haze content. The compositions of this invention may also contain elemental metals, such as antimony, and a reducing agent, to further increase the PET""s heat-up rate. If no element metals are used, the composition may still include a non-reducing stabilizer to increase the PET""s heat-up rate.
Thus, the present invention generally provides a composition of matter comprising a thermoplastic polymer, an inert iron compound having no chemical reactivity to the thermoplastic polymer, and an elemental metal.
One or more other aspects of the present invention may be found in a composition of matter comprising a thermoplastic polymer, an inert iron compound having no chemical reactivity to the thermoplastic polymer, and a phosphorus stabilizer in either the trivalent or pentavalent state.
Still other possible aspects of the present invention may be provided by a blend of PET with one or more of FeP, Fe2P, Fe3P, and FeSi; an antimony catalyst; and a phosphite or a phosphate.
At least one or more of the advantages of the present invention over the known art relating to thermoplastic polymers, which shall become apparent from the specification as follows, are accomplished by the invention as hereinafter described and claimed.